1. Field of the Invention
The invention relates to methods of isolating microorganisms and more particularly to an improved method of isolating polysaccharide producing microorganisms.
2. Brief Description of Related Art
It is desired to improve the prior art relating to the biological production of polysaccharides.
Gellan, for example, is a microbial anionic heteropolysaccharide composed of tetrasaccharide units produced by Auromonas elodea ATCC 31461. Native gellan is substituted by acetyl and L-glyceric acid radicals. These substituents can be eliminated readily by treatment with alkali. The resulting unsubstituted gellan (named hereinafter gellan/u) is a product of industrial interest which has the physical property of thermoreversibly forming gels in aqueous solutions. Gellan/u is already marketed as an agar substitute (Gelrite, manufactured by Kelco, Rahway/USA). A wide range of applications is feasible for the food industry. Approval of a food additive has already been applied for in the USA and in Europe; see V. J. Morris, Food Biotechnology 4 (1990) No. 1, p. 45-57. In Japan, gellan was approved as a food additive as early as 1988; see V. J. Morris, supra.
Bacterial species in which the formation of a polysaccharide such as, for example, gellan, has been observed, are known. The difficulty arising from the use of such species for the production of polysaccharides is that not all strains, clones or cells of this species produce the desired polysaccharide efficiently and extracellularly.
Surprisingly, it has now been found that cells which produce gellan extracellularly do not sink into a gellan matrix, while cells which do not produce gellan extracellularly submerge in the gellan matrix. Starting from the abovementioned observation, a method has now been developed by means of which cells and clones can be isolated which produce a desired polysaccharide, such as gellan, efficiently and extracellularly.